The present invention is related to pulse generation. More particularly, the present invention is related to a system and method for generating a pulse using a single comparator and supporting logic. Delays for activating the pulse are matched by delays for deactivating the pulse such that the pulse width is carefully controlled.
DC-DC converters are switching regulators that typically employ pulse-width modulation (PWM) control. The converter is arranged to control the on-time of a switching element. The output of the switching element is a pulsed input voltage (VIN) that is coupled to a filter network such as an L-C filter. The L-C filter stores energy from the voltage pulse to provide an average output voltage (VOUT). The average output voltage is related to the pulsed input voltage (VIN) by the pulse on-time (TON) and the period of the pulse (TP) as given by: VOUT=VIN*TON/TP. By varying the on-time (TON) of the pulsed input voltage (VIN), the average output voltage (VOUT) can be adjusted.
During the on-time, the switching element is activated such that input voltage (VIN) is connected to the inductor (L). The difference between the input voltage (VIN) and the output voltage (VOUT) is forced across the inductor, causing the current flow through the inductor to increase. During the on-time, current is delivered to the capacitor (C) and the load through the inductor. The output voltage (VOUT) increases as current is delivered to the capacitor (C).
During the off-time, voltage applied to the inductor is removed. Since current in an inductor cannot change instantaneously, the voltage across the inductor will adjust to hold the current constant. A freewheeling diode is typically connected in parallel with the L-C filter circuit. The input end of the inductor is forced negative in voltage by the decreasing current, eventually reaching the point where the diode is turned on. The inductor current then flows through the load and back through the diode. The capacitor discharges into the load during the off time, contributing to the total current being supplied to the load. The total load current during the switch off-time corresponds to the sum of the inductor and capacitor current.